1. Field of the Invention
This invention relates generally to loading data into integrated circuit devices. More particularly, this invention relates to enabling and configuring a plurality of field programmable gate arrays.
2. Description of the Related Art
In the electronics industry, field-programmable devices such as Field-Programmable Gate Arrays (FPGAs) have emerged as efficient tools for quick product development and low-cost prototyping. An FPGA consists of an array of uncommitted elements that can be interconnected in a general way. The interconnections between the elements are user-programmable.
FIG. 1 shows a prior art conceptual diagram of a typical FPGA. As depicted, it consists of a two-dimensional array of logic blocks that can be connected by general interconnection resources. The interconnect comprises segments of wire, where the segments may be of various lengths, and switches that serve to connect the logic blocks to the wire segments, or one wire segment to another. Logic circuits are implemented in the FPGA by partitioning the logic into individual logic blocks and then interconnecting the blocks as required via the switches.
The FPGA-assisted design process begins with initial logic entry of the circuit to be implemented. This is normally done using a computer-assisted design tool. The expression of the logic entry is then transformed, or mapped, into a circuit of FPGA logic blocks 6, as illustrated in FIG. 1. Once the logic is mapped into logic blocks, it is necessary to decide where to place each block in the FPGA's array. Once placement is completed, routing between circuit elements is required. Routing software assigns the FPGA's wire segments 14 and chooses programmable switches to establish the required connections among the logic blocks and to configure input/output blocks
Upon successful completion of the placement and routing steps, the design system's output is fed to a configuring unit, which configures the final FPGA device with the configuration data. To implement a desired circuit, the FPGA must be given the information as to what connections are to be made and/or what logic is to be implemented. This is generally accomplished by employing a configuration bitstream.
The configuration bitstream is generally used to configure switches inside the FPGA to a desired state, (e.g., on or off). These switches can be implemented from RAM cells which control pass transistors, antifuse connection points, fuse connection points, or any other type of switch implementation. These switches are then used to control the configurable routing or logic on the FPGA. Configuration of the FPGA empowers the user to create any one of myriad possible circuit layouts on a unitary device or a group of devices.
When a design requires more than one FPGA, there are several options for storing configuration data and loading the final configuration data into an FPGA device. For example, in one known method of loading configuration data into a plurality of FPGAs, multiple devices are serially connected with data transfer lines and configured through a data bus connected only to the first device in the chain. When the first device has configured, additional data is directed through the first device and into the second device, where the procedure repeats until all devices are fully loaded.
While this technique is commonly used, at least two flaws are readily apparent. First, serial flow of data is rather slow when compared to parallel data flow. Second, the process is further prolonged by the need to run data through all preceding devices before the data reaches its intended device destination. Slow data flow also ties up the data bus, a crucial thoroughfare which could be used for other data processing functions, such as I/O or addressing, instead of waiting for the cascading flow of configuration data to conclude.
As the size or gate count of FPGAs increases, the number of switches in an FPGA will increase appreciably. As a consequence, the configuration bitstream becomes larger, making the bitstream difficult to manage and move through a transfer line quickly. The amount of time required to configure the FPGA becomes more burdensome during device testing where it is common to reconfigure the FPGA many times. Therefore, the industry requires a method and structure to reduce the time required to configure FPGAs, especially in systems having multiple FPGAs.
One possible method for accelerating the flow of data is the use of parallel data flow instead of serial flow. While one could send parallel data from the data bus to the devices, the data transfer line device interconnect would require the dedication of a large number of I/O device pins to the configuration function. Moreover, these dedicated I/O pins would be further constrained to chip-to-chip data transfer.
Alternatively, one could avoid the cascading data approach entirely by sending the data stream to only one device at a time directly from the data bus. However, this technique would require an additional decode means or other means, possibly external to the FPGA devices for independently controlling each device.
There is, therefore, a need for a system and method for loading data into a plurality of integrated circuit devices which allows for independent access to each device from a common data source, but which does not depend on control means external to the devices to ensure data reaches an intended device.